Mannerheim was
christened Carl Gustaf Emil, but was called by his middle name Gustaf.

Throughout his whole life he signed his private letters Gustaf or G. Mannerheim. According
to the military custom, he often signed the official documents using only his military
rank or his family name.

In Russian service,
Mannerheim was called by his first name and his fathers name, Gustaf Karlovich,
which was a Russian custom. Because of his first Christian name Carl, the name Karl
Gustafovich appeared in official documents at one stage in the 1890s. As Regent in 1919,
he used the forename Kustaa, the Finnish form of Gustaf.

On his journey from Helsinki to Vaasa in January 1918, he
used the name Gustaf Malmström for security reasons. The activists of the so-called New
Forest Office, who were obliged to use codes and code names in their activitites, named
him Andersson. In the parlance of some young Agrarians he was called by a code name
Gospodin, which referred to his aristocratic attitude and the Russian influence in a
somewhat critical tone.